Monitoring heart rate and sleep is something these fitness trackers do very well

Most fitness trackers also track sleep, but reviewers say the Jawbone UP24(Est. $100) is a standout for its unique ability to spot an ideal waking moment based on your REM cycles. It also features a power-nap switch that analyzes your sleep habits to determine what your best nap length is -- and then wakes you with a silent alarm.

In addition to its in-depth sleep tracking, the Jawbone UP24 is a favorite among reviewers for its superb fitness app, which is compatible with iPhone and Android devices. Like Fitbit, it allows you to scan food barcodes to input nutrition information. The app can turn your activities into games by linking your data with your friends', encouraging friendly competition. A unique mood-tracking app lets you input how you feel at various points during the day -- after eating, sleeping, or exercising, for example. User say this helps them identify patterns and maximize those things that boost mood, minimize those that don't. In general, say reviewers, the Jawbone UP24 offers more information overall than other fitness trackers to help you interpret your own fitness data; it also receives kudos for its fun daily health tips.

Where the UP24 falters is when it comes to accessing the data. There's no built-in screen, so users must look at their smartphone to read their daily progress. However, unlike the original Jawbone UP (Est. $75), which is discontinued but still can be found at retail, the UP24 does sync with Bluetooth, so it no longer has to be tethered in order to upload data. Another missing feature: There is no desktop app, and many reviewers lament that they can't access their data when working at their computer.

Still, for some people, sleep tracking is their top priority, and the Jawbone UP24 is phenomenal at analyzing the subtle gradations of the sleep cycle. That, combined with its great fitness app, makes the Jawbone UP the logical choice for those who are serious about sleep.

As for heart monitoring, we suggest you consider the newly-introduced Basis Peak(Est. $200). It came close to knocking out the Fitbit One as our top choice overall based upon expert reviews, but users aren't as taken with it so we're going to wait and see how the Peak shakes out over the long term. Many experts put the Peak at the top of their "best of" lists -- ahead of the Fitbit One -- saying they love its fully automated detection that knows when you're walking, running, riding a bike, or sleeping. You never have to set it for any particular "mode," it figures it out and lets you know it's figured it out by showing you an icon for your activity on the screen.

Unfortunately, say users, it's "not quite ready for primetime" as an all-purpose fitness tracker. There are a lot of very detailed reviews from owners who are extremely knowledgeable about fitness trackers and they note some flaws with this Basis. There are no alarms available, which even the most basic fitness trackers usually have; it seems to miss steps when the arms aren't involved (like pushing a stroller or cart); and there's a lack of third party integration. In addition, owners say, they would like to be able to customize the display to give them the option to view metrics, rather than a default to the clock. It gets mixed reviews for sleep tracking, as well, some say it's excellent; others say it's automated system is sometimes wrong about when they actually fall asleep and they'd prefer being able to set it -- as you can with the Jawbone UP24.

The reason the Basis Peak is rated so highly by experts is because of its potential. Basis has said that firmware updates in the near future will address many of the aforementioned glitches. Smartwatch features such as text messages and other notifications are also on the "coming soon" list. These promised, as opposed to existing, features and fixes are the reason that knowledgeable users say it seems as if the Peak was rushed to the market.

However, all agree that the Peak excels at tracking biometrics like heart rate, skin temperature, perspiration and calories burned. Serious fitness buffs like to know the effect of exercise on their heart rate, and also keep track of their resting heart rate, and experts say that, right now, the Peak is the best, most versatile device for doing so, with enough potential that it may be the best deal in smart fitness trackers.

The Withings Pulse(Est. $100) also offers a built-in heart monitor. It's not continuous monitoring like the Basic, but reviewers say the feature is rare enough at this price point to make it a great value, and it's not difficult to do: Users hold their finger over the sensor for a few seconds to record beats per minute. It can also measure blood oxygen levels.

The Pulse has some other attractive features as well. The OLED display gives instant feedback on the time and distance of the current workout and lets users scroll through activity logs. The device itself is sleek and compact, easily fitting into a pocket. The Pulse includes a silicone clip that comfortably attaches to clothing, as well as a wristband, which give it versatile wear options. The Withings may be a particularly good option for runners because it excels at recognizing running and has several useful setting for displaying your stats.

However, we read too many reviews questioning the Pulse's reliability to give it a glowing recommendation. Many users say it failed very quickly, is less water resistant than the manufacturer indicates, and that customer service is unresponsive. However, when it works as it should, users love it.

Elsewhere in this Report:

Best Reviewed Fitness Trackers: Which are the best activity trackers? Editors identify top the top fitness trackers and suggest the best picks for your activities and lifestyle.

Best Fitness Trackers: These fitness trackers monitor your activities, steps, calorie expenditure and more. We recommend the best activity tracker for any lifestyle.

Buying Guide: What kind of fitness tracker do you need? Here is your guide to determining which type of activity tracker will best suit your exercise habits and lifestyle.

Our Sources: We used these professional and user review sources to find the fitness trackers. They are ranked in order of their expertise and helpfulness.

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